Studies of the wetting kinetics of liquid drops on solid surfaces
The viscosityηL and the surface tensionγL of the liquid as well as the equilibrium contact angleθe are essential parameters governing the wetting kinetics of liquids on solids. By means of a contact angle apparatus with video image digitization, the dynamic contact angle θ and the radiusr of the contact area of sessile drops on solid surfaces have simultaneously been determined in dependence on time after drop application between about 3·10−2 s and long times.
The measurements were performed with series of liquids: polydimethylsiloxanes with different molecular masses and solutions of polyisobutylene in decalin and polyacrylic acid in water, covering a wide range of concentrations. The liquids in each series have a constant surface tension, but viscosities ranging over about four orders of magnitude, allowing the influence ofηL andγL to be studied independently. Solids such as glass, polyethylene and polytetrafluoroethylene were chosen so that the cases of complete wetting (spreading) and partial wetting (θe) could be studied.
The curves of cosθ andr/R0 vs. time for the different liquids of a series can be superimposed to a master curve by plotting them againstγL·tηL·R0, whereR0 is the radius of the original drop. All these master curves coincide at small wetting times, with exception of the data for the polysiloxanes. That means that the early stage of the wetting process is determined only by the properties of the wetting liquid. The influence of the solid surface, characterized by the equilibrium contact angleθe becomes significant only at the end of the wetting process.
Key wordsSurface tension viscosity dynamic contact angle sessile drop video image digitization
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- 1.Bascom WD (1988) Adv Polymer Sci 85:90Google Scholar
- 2.de Gennes PG (1985) Rev Modern Phys 57:827Google Scholar
- 3.van Oene H, Chang YF, Newman S (1969) J Adhesion 1:54Google Scholar
- 4.Schonhorn H, Frisch HL, Kwei TK (1966) J Appl Phys 37:4967 and (1968) J Coll Interf Sci 28:543Google Scholar
- 5.Hoffman RL (1975) J Coll Interf Sci 50:228Google Scholar
- 6.Bascom WD et al. (1964) Adv Chem Ser 43:355Google Scholar
- 7.Ghiradella H et al. (1975) J Coll Interface Sci 51:522Google Scholar
- 8.Ogarev VA et al. (1974) J Adhesion 6:337Google Scholar
- 9.Tanner LHJ (1979) Phys D: Appl Phys 12:1473Google Scholar
- 10.Marmur A (1983) Adv Coll Interface Sci 19:75Google Scholar
- 11.Lelah MD, Marmur A (1981) J Coll Interface Sci 82:518Google Scholar
- 12.Teletzke GF, Davis HT, Sciven LE (1987) Chem Eng Comm 55:41Google Scholar
- 13.Cox RG (1986) J Fluid Mech 168:169Google Scholar
- 14.Girault HH et al. (1982) J Electroanal Chem 137:207Google Scholar
- 15.Cheng P et al. (1990) Colloids a. Surfaces 43:151Google Scholar
- 16.Cazabat AM, Cohen Stuart MA (1986) J Phys Chem 90:5845Google Scholar
- 17.Foister RT (1990) J Coll Interface Sci 136:266Google Scholar
- 18.Jiang TS et al. (1979) J Coll Interface Sci 69:74Google Scholar